Compositions containing sodium percarbonate

ABSTRACT

Sodium percarbonate exhibits a tendency to decompose in built compositions and particularly detergent compositions built with zeolites. The tendency can be ameliorated by selecting sodium percarbonate which intrinsically has a mean particle size of from 500 to 1000 microns and not more than 20% by weight of below 350 microns and has a moisture pick-up when measured in a test at 80% relative humidity and 32° C. after 24 hours of not greater than 30 g/1000 g sample. A suitable sodium percarbonate can be made most conveniently by crystallisation from a bulk saturated solution of sodium percarbonate in a crystalliser/classifier that does not employ a conventional chloride salting-out agent.

This invention concerns sodium percarbonate and compositions containingit, especially detergent compositions which contain additionally aconstituent thereof which interacts destructively with sodiumpercarbonate.

Detergent compositions, and specifically particulate detergentcompositions intended for general purpose household fabric washing orfor specialist uses such as nappy sanitisation or dishwashing oftencontain in addition to one or more surfactants, a builder, a bleach andoptionally fillers/processing aids and minor amounts of a number ofother adjuvants including one or more chosen from an optical bleach,complexing agents, perfumes, and colours. Traditionally, the builder wasselected from inorganic phosphates such as sodium tripolyphosphate inview of the beneficial properties of phosphates in fabric washing, butphosphates have been shown to cause or contribute to eutrophication, andone source of phosphates is the effluent from domestic or industrialfabric washing. Consequently, and in response to increasingly stringentlegislation in various countries, the detergents industry in more recentyears has sought alternatives to phosphates, of which one very importantclass of replacement builders comprises zeolites.

The bleach constituent usually comprises a peroxygen compound, of whichone favoured example comprises sodium carbonate peroxyhydrate in view ofits solubility and other characteristics. This compound has commonlybeen called sodium percarbonate, and is so referred herein. However,sodium percarbonate can interact destructively with other detergentconstituents resulting in progressive decomposition of the percarbonateand hence its loss of bleaching power during storage and transportationof the composition and the problem is especially evident when thedetergent builder comprises zeolites.

A number of proposals have been made to overcome or ameliorate theproblem of sodium percarbonate decomposition in zeolite-built detergentcompositions. In general, the proposals relate to two methods. In onemethod, as exemplified by EP-A-0451893 to Unilever, a particle sizedistribution of the sodium percarbonate is selected in accordance with agiven formula. In effect, the formula favours a mean particle size of atleast 400 microns and a narrow particle distribution. Such a methodemploys simply the gross external dimensions of the percarbonate toindicate which are superior and which are inferior particles to employ.However, sodium percarbonate generally has a porous or irregular outerlayer so that the gross dimensions do not directly control the effectivesurface area of the percarbonate. The regularity and porosity of theexternal surface of sodium percarbonate varies depending upon its methodof manufacture, and this is a further and very important factor whichdirectly affects the effective surface area and the stability of thepercarbonate.

A second and frequently described method of improving the stability ofsodium percarbonate is to coat the surface of the percarbonate with asurface layer of material which physically interposes itself between thesurface of the percarbonate and any other particulate constituents ofthe composition. The effectiveness of the coating at retarding orameliorating the rate and extent of percarbonate decomposition dependson the nature of the material employed for the coating and the integrityof the coating. Whilst a number of coating materials have been describedwhich are beneficial in retarding decomposition in zeolite-builtdetergent compositions, including particularly coatings containingsodium borates in U.S. Pat. No. 4526698 to Kao Soap, these do not teachthe reader anything about the inherent stability of the uncoatedpercarbonate. Likewise, in WO 95/15291 to Kemira, there is described theuse of carbon dioxide gas in contact with damp percarbonate during thecoating operation to improve the resultant stability of the resultantcoated percarbonate. As with the Kao Soap disclosure, this provides noteaching on the stability of the uncoated percarbonate.

The continuing desire to incorporate both zeolites and sodiumpercarbonate in a detergent composition, and especially in concentratedor ultra-concentrated detergent compositions means that there remains acontinuing need to find yet more and/or better ways to improve thestability of percarbonate and/or determine how to select appropriatelyfrom the various manufacture methods for sodium percarbonate, theproduct which exhibits improved or optimised stability.

In addition, however, at least in some parts of the world, a significantfraction of washing compositions or bleach additive compositions arebuilt with a major proportion of non-zeolite builder or even without anyzeolite builder, so that it would also be commercially advantageous toimprove or optimise the stability of sodium percarbonate incorporated insuch compositions too.

It is a first object of at least some aspects of the present inventionto provide other and/or improved detergent compositions containing bothsodium percarbonate and a zeolite.

It is a further object of the present invention in at least certainother aspects to identify a method of selecting sodium percarbonatewhich is intrinsically suited for incorporation in built compositions.

According to the present invention, there is provided a detergentcomposition which contains a zeolitic builder and sodium percarbonatecharacterised in that the sodium percarbonate intrinsically has a meanparticle size of from 500 to 1000 microns and not more than 20% byweight of below 350 microns and has a moisture pick-up when measured ina test conducted in a humidity room at 80% relative humidity and 32° C.after 24 hours of not greater than 30 g/1000 g sample.

Herein, “intrinsically” when employed in conjunction with sodiumpercarbonate or “intrinsic sodium percarbonate” both indicate dry sodiumpercarbonate which has been obtained from a crystallisation or othermanufacturing process without a subsequent coating or surface treatmentthat has to interpose a layer of non-sodium percarbonate materialbetween itself and some other constituent of the composition. It will berecognised that the properties of particulate sodium percarbonate can bemodified by subsequent treatments, but that it remains advantageous toselect as core material, sodium percarbonate that has good stabilityintrinsically.

According to a further aspect there is provided a process for selectingsodium percarbonate for incorporation in a builder-containingcomposition characterised by conducting in either order the steps of

1) measuring its particle size distribution, determining its meanparticle size and the weight fraction below 350 microns, and rejectingfrom step 1 material which has a mean particle size outside the range offrom 500 to 1000 microns or contains more than 20% by weight of below350 microns; and

2) measuring the extent to which moisture is picked up by the materialin a test conducted for 24 hours at 32C and 80% relative humidity andrejecting material which picks up more than 30 g moisture per 1000 gmaterial, the retained material meeting acceptable standardsintrinsically for sodium percarbonate in regard to its particle size andmoisture pick-up.

By selecting intrinsic sodium percarbonate which simultaneously has adesirable particle size distribution and a suitable moisture pick-up inthe specified tests, it is possible to identify sodium percarbonatewhich has a superior stability in a built composition such as especiallya zeolite-built detergent composition when compared for example with theincorporation of commercially available uncoated percarbonate whichmeets neither or only one of the selected parameters.

It will be recognised that it is possible to produce and isolate variedsodium percarbonate products having the same or similar particle sizedistribution, but a widely differing moisture pick-ups by the choice ofmanufacturing process and by appropriate selection ofconditions/operating parameters within the chosen manufacturing process.Such varied products have varying stability to decomposition in a builtcomposition, and especially a zeolite-built detergent composition. Somewill be better and some will be worse, and the choice of which sodiumpercarbonate is better to use can be made by employing the inventiontwin test method.

Without being bound by any particular theory or belief, it is consideredprobable that the moisture pick-up as measured by the test is indicativeof the extent of irregularity and/or porosity of the sodium percarbonatethat is presented to the atmosphere, whereas the particle sizedistribution is indicative of the physical contact between particulateconstituents of the composition and that when taken together rather thanindividually, the two tests present a clear basis for selecting sodiumpercarbonate intrinsically having relatively good stability in thepresence of zeolite builder, and In fact, in the presence of otherbuilders too.

It is preferable for the sodium percarbonate particles to fallsubstantially within the range of from 250 to 1250 microns andparticularly for at least 80%, and advantageously at least 95%, byweight of the particles to fall in the range of 350 to 1000 microns. Itis particularly desirable to employ sodium percarbonate which has a meanparticle size of from 550 to 850 microns and in a number of preferredembodiments of from 600 to 800 microns. A product having a mean particlesize of at least 600 microns and especially at least 650 microns and aspan of from 0.9 to 1.2 will often meet the particle size criteriawithout further classifying being carried out. From the standpoint ofpercarbonate stability, it is desirable to avoid or minimise theproportion of relatively small particles, such as particles of below 350microns and particularly below 250 microns. The relatively largeparticles such as over 1000 microns diameter do not impair stability,but can segregate from the smaller constituents of the compositions to agreater extent.

The particle size distribution of particulate sodium percarbonate can bedetermined by a standard method of sieving a representative sample ofthe material through a nest of sieves of known decreasing aperture, andweighing the fraction of material retained on each sieve. As the numberof sieves increases, the accuracy of the measurement increases. In analternative method of measurement, the particulate product is passedthrough a beam of light from a laser and the resultant scattered lightis analysed, for example using a particle size analyser available underthe tradename Malvern 2600 C.

The particle size distributions that are indicated herein can beobtained by one or more of the following methods. Where acrystallisation process is employed, external classification of forexample dried percarbonate and/or an integrated internal classifierlinked to the crystalliser and classifying the percarbonate particles ina liquid medium can be employed respectively to isolate the requiredfraction or manufacture a desired range of percarbonate particles. Forexample, a product having a mean particle size of dried particles withinthe range of 500 to 700 microns can readily be obtained from a driedproduct of a conventional “wet” manufacturing process by sieving andexcluding substantially all particles below a specified sieve size, suchas 350 microns, thereby leaving a fraction that extends typically from350 to about 850 microns and a peak fraction at around 500 to 600microns. By sieving to exclude product below a higher sieve size, eg500μ, it is possible to obtain a product with a higher mean particlesize of eg 600 to 700. Alternatively or additionally, particles inexcess of an upper size such as 1250 or 1000 microns can be removed soas to leave a narrower range. It will also be recognised that theparticle size distribution of product obtained in manufacture processescan be varied by controlling the process parameters. Hence, in acrystallisation process, by controlling the rate of nucleation relativeto growth in the crystalliser and avoiding or minimising theintroduction of preformed nuclei, it is possible to increase the averageparticle size of the resultant product.

In a further variation, the particle size distribution of sodiumpercarbonate having a mean particle size of below 500 μ can increased towithin the desired range by a process of granulation/agglomeration ofthe particles, typically with the aid of an aqueous solution of a knownagglomerating/granulating aid for alkaline materials sprayed onto thepercarbonate in conventional apparatus, such as a granulating pan. Forexample, water-soluble coating agents for sodium percarbonate, such assilicate, can be suitably employed under the process conditionsappropriate for granulation to bind the percarbonate particles togetherrather than simply form a coating.

It is especially preferable to employ crystallised sodium percarbonatewhich has been produced by a process in which a classifier is integralwith the crystalliser, and operated such that particles above and belowa desired minimum size are separated out in the classifier, the largerparticles are recovered as product whereas the smaller particles arerecycled to the crystalliser where they can grow as a result ofdeposition of additional sodium percarbonate from solution, typically byaddition of salting-out agent into saturated or supersaturated sodiumpercarbonate solution in the crystalliser, and the enlarged particlesflow back into the classifier. Such combined classifier/crystallisersare particularly beneficial in that by suitable operational control, itcan be possible to control the granulometry of the particles duringmanufacture rather than having to employ an external and henceadditional classification process. The product usually has a particledistribution which is similar to “normal”, the spread for which dependson the type of plant employed. It often has a span of from about 0.6 toabout 0.9. The product usually displays at least 80% and frequently atleast 90% of its particles by weight within the range of +/−50% of themean particle size, with mean particle size of above 600 to 1000 and inmany instances from 650 to 850 microns.

A further process capable of producing sodium percarbonate with thedesired particle size range comprises a crystallisation process operatedwith the ratio of hydrogen peroxide to sodium carbonate keptsubstoichiometric, and particularly in the range of 0.8-1.2:1, motherliquor on recycle to the crystalliser being less than saturated incarbonate, and the crystallisation being carried out without addition ofsalting out agent.

Advantageously, the processes that avoid a salting out agent like sodiumchloride which is readily co-precipitated with sodium percarbonate, andparticularly processes which avoid salting out agent can produce producthaving a high purity, for example having an Avox of at least 14.5% andin some embodiments an avox of at least 14.8%.

Such crystallisation processes above can naturally be carried out usingstabilisers and crystal habit modifiers such as sodium silicatepolyphosphonic acids, phosphates and homo or copolyacrylates in themanner recognised by the art, though with heightened benefit whensalting out is not employed so that residual concentrations of peroxidecan be higher than in chloride-salted processes. In many instances, theresultant product has a smooth round shape which encourages closepacking and enables its bulk density to fall the region of 800 to 1100g/1000 g in a standard free flowing bulk density test.

Alternatively, where for example particulate sodium percarbonate isobtained by evaporating a carrier fluid from a solution of sodiumpercarbonate, or solutions of the reactants to form in situ sodiumpercarbonate, that is/are respectively sprayed onto a bed of sodiumpercarbonate particles, for example fluidised by an updraft of dryinginert gas, eg air, the process operation can be continued until thedesired particles are obtained having at least a minimum size thatprovides the mean particle size with at least the broadest range of 500to 1000 microns. In such a fluidised bed process, it is possible toselect operating conditions which reduce or minimise the creation ofnuclei by in situ physical disintegration of existing particles in thebed and minimise the introduction of externally produced nuclei, therebyonce again promoting the formation of a product having a larger particlesize.

A second important characteristic of the sodium percarbonate employed inthe invention compositions is the extent/rate at which it picks upmoisture from a humid atmosphere. Herein, including specifically in theexemplified and comparison compositions, the capability of the sodiumpercarbonate to pick up moisture is measured by the following test:

A 9 cm diameter petri dish with a 1 cm depth rim is weighed accuratelyon a 4 decimal place balance, (W1). A sample of dry sodium percarbonate(about 5 g) is placed on the petri dish which is gently agitated togenerate an even particulate layer across the base of the dish andreweighed on the same balance, (W2). The sample on the petri dish isstored in a room, about 3 M high, wide and long in an atmospheremaintained for a period of 24 hours at 32° C. by a thermostat controlledheater and at 80% Relative Humidity (RH) by introduction of a finedroplet water spray under the control of an humidity detector andweighed on the same balance, (W3). The samples are protected by a shieldfrom the spray.

The moisture pick-up of the sodium percarbonate is calculated asfollows:${\text{Moisture~~~~Pick-up}\quad \left( {g/{kg}} \right)} = \frac{\left. {1000 \times \left( {{W3} - {W2}} \right)} \right)}{\left( {{W2} - {W1}} \right)}$

Depending on its method of manufacture, the extent of moisture pick-upby sodium percarbonate in the test can vary over a very wide range, froma low figure that is below 10 g/1000 g such as from 1-5 g/1000 g up to afigure that is in the range of from 100 to 200 g/1000 g. Such latterproducts are outside the scope of the instant invention. Othermanufacture methods can generate products having a moisture pick-up ofbetween 15 and 30 g/1000 g in the test. Their use in zeolitecompositions is according to the present invention, though the selectionof products with lower (ie up to 15 g/100 g) or especially the lowestmoisture pick-up are preferred.

It has been found that the extent of moisture pick-up is influenced bywhich substances, such as salting-out agents, are employed to promotecrystallisation of the percarbonate. Traditionally, the most importantsalting out agent has been sodium chloride, because it is readilyavailable and has been very effective for promoting crystallisation, butit is now found, disadvantageously, that its use tends to promote theextent of moisture pick-up. Consequently, and in order to control themoisture pick-up of intrinsic sodium percarbonate, it is especiallydesirable that the proportion of sodium chloride in the salting outagent be controlled to provide at most no more than a minor fraction ofthe sodium (on a molar basis), such as for example not more than 10%. Itis particularly desirable to employ an essentially chloride-freesalting-out agent, ie at no more than an impurity level. In certainparticularly preferred processes for obtaining sodium percarbonatehaving the desired low moisture pick-up characteristic, sodium sulphateis employed as salting out agent. In other especially suitable processesfor producing a product having a low-moisture pick-up, thecrystallisation can be carried out in the absence or substantial absenceof any added salting out agent, for example by omission of the saltingagent from the process described in EP-A-0703190.

It will correspondingly be recognised that if a coating agent is used,at least in part, to granulate intrinsically acceptable sodiumpercarbonate to increase its mean particle to above 500 μm,corresponding restrictions on the presence of chloride in the coatingagent are desirable.

It will be recognised that it is especially advantageous to the sodiumpercarbonate manufacturer to employ a manufacturing process for thesodium percarbonate which can be controlled to produce a product havingsimultaneously a low moisture pick-up and a narrow particle sizedistribution with a mean in the region of 500 to 1000 microns. Such amanufacturing process employs in combination crystallisation ofpercarbonate in an integrated crystalliser/classifier as describedherein and the use of sodium sulphate or like other non-chloride sodiumsalt as the salting out agent. Indeed, within the class of especiallysuitable processes are those in which a salting out agent is omitted.

One type of apparatus, which can advantageously be employed to producesodium percarbonate having intrinsically acceptable properties, providedthat an appropriate choice is made of salting out agent, if any is used,is described in EP-A-703190 to Solvay Interox SA.

The detergent composition of the present invention often contains sodiumpercarbonate meeting the combination of mean particle size from 500 to1000 μ and moisture pickup of not more than 30 g/1000 g in the test inan amount of least 2% and in many instances at least 5% by weight. It isusually not more than 40% and in many instances up to about 25% byweight of the composition.

It will be recognised that the sodium percarbonate having theaforestated combination of defined particle size and moisture pick-upcharacteristics can be incorporated as such in the zeolitic or otherbuilt detergent composition or optionally it can serve as a convenientand preferred base for coating so as to combine further its inherentstability with that imparted by a coating. The amount of such a coatingis selected usually in the range of from 0 to 20% w/w based on thesodium percarbonate and a convenient amount is often selected in therange of from 1 to 5% w/w. It is especially desirable to select thecoating material such that it augments rather than undoes theimprovement in stability achieved by the inherent sodium percarbonate.In consequence, it is preferable to employ a coating which excludes asoluble halide such as especially sodium chloride from the coating ordoes not employ more than an acceptable upper amount, such as not morethan about 2.5% based on the sodium percarbonate. Subject to therestriction concerning chloride, the coating materials oftenadvantageously comprise one or more materials selected from thefollowing: Alkali metal and/or alkaline earth metal, particularly sodiumor soluble magnesium, salts of mineral or other inorganic acids andespecially sulphate, carbonate, bicarbonate, phosphate and/or polymericphosphates, silicates, borates and the corresponding boric acids. Thecoating can additionally or alternatively include water soluble acidsand salts of metal chelating agents such as in the classes ofaminoethylenepolycarboxylates andaminoethylenepolymethylenephosphonates, including the well known EDTA,DTPA, EDTMPA and DTPMPA, and/or chelating carboxylic orhydroxycarboxylic acids, such as citrate, tartrate or gluconate. Otherconstituents can include fatty acids (eg up to C20) and/or thecorresponding amides.

Particular combinations of coating agents of note includecarbonate/sulphate, and boric acid or borate with sulphate and thecombination of a) sulphate, carbonate/sulphate, bicarbonate, boric acidor borate alone or with sulphate, citrate or citrate/sulphate, gluconateor gluconate/sulphate, with b) silicate and/or a carboxylate orphosphonate metal chelating agent.

A wide range of zeolite builders, sometimes alternatively referred to asaluminosilicate builders, can be incorporated in the inventioncompositions. Suitable zeolites usually demonstrate a substantialcalcium (or other alkaline earth metal) (ie water hardness) ion exchangecapacity, expressed as CaCO₃ equivalent of at least 150 mg CaCO₃ per gand for most of the preferred zeolites their hardness exchange capacityof from 200 to about 350 mg CaCO₃ equivalent per g.

A number of such zeolites often obey the empirical general formulaM_(z)[(AlO₂)_(z)(SiO₂)_(y)] xH₂O in which M represents an alkali metal,preferably sodium, z and y are both at least 6 and the mole ratio of y:zfrom 1:1 to 2:1 and x is at least 5 and preferably from 10 to about 280.Many of the zeolites are hydrated, containing up to about 30% by weightof water, such as from about 10 to about 25% water bound within thematerial. The zeolites can also be amorphous, though a majority ofpreferred zeolites are crystalline.

Although certain aluminosilicates are naturally occurring, most aresynthetic. Suitable named crystalline zeolites of well known structureand formula include zeolite A, zeolite X, Zeolite B, zeolite P, zeoliteY, zeolite HS, and zeolite MAP.

The proportion of zeolite in the composition is often at least 5%, andin many instances at least 10% by weight thereof. it is normally notgreater than about 60%, often not greater than 50% and in many instancesnot more than 40% by weight of the composition.

Zeolite for use in the present invention can be prepared in a way whichreduces or minimises subsequent attack on bleach in a composition, suchas by control of the moisture content, preferably below equilibriumlevel, as described for example in WO 95/05445.

It will be understood that, in a modification to the invention, althoughthe instant invention in one aspect is directed primarily atcompositions containing one or more zeolite builders in conjunction withthe selected percarbonate, a similar benefit in terms of improvedpercarbonate stability can be observed by selecting the percarbonate inthe same way for use in conjunction with amorphous or especially layeredsilicates to be substituted for the zeolite within the same weightproportions, though on a lesser scale as befits their more benigninteraction with percarbonate . Such layered crystalline silicates oftenobey the empirical formula Na₂Si_(x)O_(2x+1).yH₂O or the correspondingcompounds in which one sodium ion is replaced by hydrogen, in which x isselected in the range of from 1.9 to 4 and y is selected in the range offrom 0 to 20, as for example disclosed in EP-A-164514. In themodification to the invention, such layered silicates are employed inthe absence of zeolites.

The detergent compositions of the present invention contain usually oneor more surfactants, often present in total in an amount of from 2 to40%, and particularly 5 to 25% by weight.

The surfactants for incorporation in solid compositions of the presentinvention can be selected from particulate or flaky anionic, cationic,non-ionic, zwitterionic, amphoteric and ampholytic surfactants and canbe either natural soaps or synthetic. A number of suitable surfactantsare described in chapter 2 of Synthetic Detergents by A Davidsohn and BM Milwidsky (6th edition) published in 1978 by George Godwin Ltd andJohn Wiley & Sons, incorporated herein by reference. Without limiting tothese surfactants, representative sub-classes of anionic surfactants arecarboxylic acid soaps, alkyl aryl sulphonates, olefin sulphonates,linear alkane sulphonates, hydroxy-alkane sulphonates, long chain andOXO alcohol sulphates, sulphated glycerides, sulphated ethers,sulpho-succinates, alkane sulphonates, phosphate esters, sucrose estersand anionic fluorosurfactants; representative classes of cationicsurfactants include quaternary ammonium or quaternary pyridinium saltscontaining at least one hydrophobic alkyl or aralkyl group,representative classes of non-ionic surfactants include condensates of along chain alkanol with either polyethylene oxides or with phenols, orcondensates of long chain carboxylic acids or amines or amides withpolyethylene oxide, and related compounds in which the long chain moietyis condensed with an aliphatic polyol such as sorbitol or condensationproducts of ethylene and propylene oxides or fatty acid alkanolamidesand fatty acid amine oxides; representative classes ofamphoteric/zwitterionic surfactants include sulphonium and phophoniumsurfactants, optionally substituted by an anionic solubilising group.The proportion of surfactant, expressed as a fraction of all thesurfactant present is often from {fraction (2/10)} to {fraction(8/10)}ths anionic, from 0 to {fraction (6/10)}ths non-ionic, and from 0to {fraction (3/10)}ths for the other surfactants.

The zeolite need not comprise the entire builder content of thecomposition and indeed in certain aspects need not be present at all.Such non-zeolite builders can be present within the conventional rangefor builders, ie from about 5 to 60%. It is essential, however, that toaccord with the present invention, the sodium percarbonate is selectedby virtue of passing the twin selection tests, namely the specifiedmoisture pick-up and particle size distribution. Other detergentbuilders that are suitable for inclusion in compositions according tothe present invention include specifically the aforementioned layeredsilicates, alkali metal phosphates, particularly tripolyphosphate butalso tetrapyrophosphate and hexametaphosphate, especially the sodiumsalt of each, alkali metal, preferably, sodium carbonate, alkali metalsilicates and alkali metal, preferably, sodium borates. Yet a furtherclass of builders which can be incorporated comprises organic chelatingbuilders such as aminopolycarboxylates andaminopolymethylenephosphonates or hydroxyphosphonates including nitrilotriacetate or trimethylene phosphonate, ethylene diamine tertraacetateor tetramethylene phosphonate, diethylenetriamine pentamethylenephosphonate or cyclohexane-1,2-diaminetetramethylene phosphonate,normally completely or partly in sodium salt form. Chelating carboxylatebuilders comprise monomeric and oligomeric carboxylates includingglycolic acid and ether derivatives, a salts and derivatives of succinicand tartaric acid, citrates, carboxy derivatives of succinates, andpolyaspartates. Others include ethane or propane tetracarboxylates andvarious sulphosuccinates. Such chelating builders can be employed in arelatively small amount as an augmenting builder and peroxygenstabiliser, such as of 1 to 10%. The additional builders including thechelating builders, can be present in amounts at the discretion of theproducer of the composition, and in total, they represent up to not morethan about 40% by weight and in many instances from about 5 to about 20%by weight.

Further and optional constituents of the detergent composition caninclude anti-redeposition and soil suspension agents, bleach activators,optical brightening agents, soil release agents, suds controllers,enzymes, fabric softening agents, perfumes, colours and processing aids.In total the optional constituents often comprise up to about 20% of thecomposition weight, and often up to 10% by weight, excluding processingaids which can additionally constitute, if desired from 0 to 30% of thecomposition weight.

Anti-redeposition/soil suspension agents are often selected from methyl,carboxymethyl or hydroxyethyl derivatives of cellulose , orpolyvinylpyrolidones and from polycarboxylic acid polymers such ascopolymers of maleic anhydride with methacrylic acid, ethylene ormethylvinyl ether. At least 0.5% and often from 1 to 5% of such agent isconveniently present.

Bleach activators which can be included are usually O-acyl or N-acylcompounds which generate peroxyacid by reaction with the sodiumpercarbonate. Suitable classes of activators include activators a1 toa20 described in EP-A-0565017, incorporated herein by reference.Particular activators or noteworthiness include TAED, SNOBS and itsisononoyl analogue, TAGU and sugar esters. Such activators, whenemployed, are usually employed in an equivalent mole ratio to thepercarbonate of from 2:1 to 1:10, and often at or around 1:1 or 1:5 to1:8. In many instances this can correspond to a content of between 1 and8% and especially 2 to 6% by weight of the composition. The user canfurther contemplate incorporating one or manganese, cobalt or titaniumcomplexes, otherwise called accelerators, in accordance with publishedliterature optionally with a calcium promoter.

Optical brightening agents are often selected from appropriatelysubstituted aminostilbenes and especially from triazinaminostilbenes.

Soil release agents are often selected form copolymers of terephthalicacid and polyethylene oxide and/or polypropylene oxide.

Suds suppressers are often silicones or alkylated silicone materials orfinely divided aerogels or xerogels of silica.

Enzymes can be selected from amylases, neutral or alkaline proteases,lipases, esterases, and cellulases which are offered commercially.

Fabric softening agents include smectite clays and water-insolubletertiary amines, sometimes in conjunction with long chain quaternaryammonium salts and/or high molecular weight polyethylene oxides. Thetotal content of such agents is often selected in the range of from 5 to15% by weight, with the organic component providing from about 0.1 to 2%by weight.

The processing aids are often selected from sodium and/or magnesiumsulphate. In concentrated or ultra-concentrated compositions, they oftenconstitute a relatively small proportion of up to about 5%, but intraditional powders, they can often constitute from 20 to 40% of theweight of the composition.

The detergent compositions of the present invention are often preparedby dry blending the particulate sodium percarbonate and sometimes afraction of the zeolite with a preformed mixture of the remainingconstituents. The mixture of the non-percarbonate/zeolite constituentscan be obtained in conventional fashion by spray drying a paste of thoseconstituents to form a particulate mixture or by agglomeration.

It will be further recognised that the benefit of selecting the sodiumpercarbonate by the twin tests for incorporation in built detergentcompositions can apply likewise to other built compositions containingthe same builders, such as for example to bleach additive compositions,which usually contain at least 5% of each of the builder andpercarbonate in a weight ratio often from 5:1 to 1:5.

Detergent compositions are produced on a bulk scale, so that theirconstituents such as sodium percarbonate in practice need to be storedin bulk and transported to the storage/detergent manufacture site inbulk. It is highly desirable to employ in detergent compositions, suchas those described hereinbefore, sodium percarbonate which has beenproduced in a crystalliser or crystalliser classifier without additionof a chloride- or in many instances particularly without any salting outagent, but which produce or can be classified to produce particulateproduct having the desirable particle size range and distributionindicated hereinbefore. It is especially desirable to select suchproducts which exhibit a very low rate of emission of heat. Arepresentative figure to enable a realistic comparison between productsproduced using different processes and in different locations can beobtained by first subjecting the percarbonate sample to a 7 day agingprocess in a sealed ampoule in a constant temperature chamber held at at40C, thereby bringing the percarbonate to substantially a plateau valuefor the heat emission. Such aging is indicated herein by reference tothe product being 7 day aged. The product is then transferred tomicrocalorimeter, model LKB 2277, also called a Thermal Activity Monitorwhich is marketed by Thermometric Limited, Sweden. The heat is measuredthat is emitted from the sample over a standard period, which herein is16 hours and at a standard test temperature which herein is 40 C. Bycomparison, a typical product obtained from a wet process involvingchloride salting out can often emit from 5 to 7 μW/g in the 16 hour testperiod, whereas the invention process products usually emit less than 3μW/g, often at least 0.5 μW/g, and in many instances from 1 to 2 μW/g.The invention products having lower heat emission can enable the sodiumpercarbonate to be handled and stored under more adverse conditions,such as in hotter climates or with reduced investment in precautionarymeans to remove heat.

It is of practical benefit to select for incorporation in detergentcompositions PCS product which not only has a large particle size,preferably with narrow span below 1, and a low MPU of below 30 g/1000 g,but has a low 7 day aged LKB of below 3 μW/g.

Having described the invention in general terms, specific embodimentsthereof are described in greater detail by way of example only.

In these Examples and Comparisons, the moisture pick-up and particlesize distribution was measured and employed as the basis for selectingthe sodium percarbonate. The data for the moisture pick-up shown wasobtained by the test at 80% relative humidity and 32° C. describedpreviously herein.

The sodium percarbonate employed in respectively Examples 1-3 wasobtained by sieving a bulk sample of sodium percarbonate produced bySolvay Interox and having a low moisture-pick up through a nest ofsieves having the mesh sizes as indicated below into three fractions.Likewise the sodium percarbonate employed in Comparisons R1 to R3 wasobtained by sieving a differently produced sodium percarbonate have amuch higher moisture pick-up through the same nest of sieves to producethree fractions. The mean particle sizes of the three pairs ofcorresponding fractions, 1 and R1, 2 and R2 and 3 and R3, were similar.

The sodium percarbonate of Examples 1-3 was obtained by acrystallisation method in which an aqueous bulk solution of sodiumpercarbonate at or near saturation was obtained by first reacting insolution hydrogen peroxide and sodium carbonate, and then introducing achloride-free salting out agent, sodium sulphate, in order to encouragecrystallisation and precipitation of the sodium percarbonate therefrom.The crystallisation process was carried out in an integrated apparatuscomprising crystalliser located above and linked to a classifier. Theliquor flowed upwards through the classifier and the crystalliser and afraction recycled to the base of the classifier. The sodium sulphatesalting out agent reduced the solubility of the solution of sodiumpercarbonate introduced into the crystalliser, thereby causing somenucleation and also deposition of percarbonate on the particles ofpercarbonate present in the crystalliser. As the particles grew in thecrystalliser they tended to fall under the influence of gravity into theclassifier below. A product comprising mainly particles of at least 400microns diameter was withdrawn from a bottom zone of the crystalliser.By virtue of the tendency for the particles sodium percarbonateparticles to fall out of the crystalliser as their size increased,rather than remain therein to further increase in size, the resultantproduct tended to enjoy a much tighter particle size distribution thanthe product of a conventional “wet” crystallisation route for makingsodium percarbonate. Consequently, although the unsieved product had amean particle size in the range of 600 to 650 microns, there wererelatively few particles of above 800 microns diameter. The product wasdried by hot air.

In the comparison compositions, the sodium percarbonate was obtained ina commercially operated “wet” manufacture route by Solvay Interox inwhich sodium percarbonate was reacted in solution with hydrogen peroxideto form a concentrated solution of sodium percarbonate, in the presenceof sodium chloride as a salting out agent in solution and the mixturewas cooled, thereby resulting in the formation of crystallinepercarbonate. Likewise, the comparison product was dried by hot air.

In the Examples and Comparisons, the detergent composition was obtainedby dry mixing 10% w/w of sodium percarbonate with 90% by weight of abase detergent composition containing zeolite A (Na) in an amount ofabout 30% w/w.

Samples (50 g) of the blended composition were transferred intopolyethylene-coated cartons which were sealed and the cartons stored ina temperature and humidity controlled cabinet at 80° F. (26.7 C), 80%relative humidity for 6 weeks. The available oxygen content (Avox) ofthe composition was measured at the beginning and end of the storageperiod, using a standard potassium-permanganate titration method and theAvox remaining at the end expressed as a percentage of its startingvalue.

TABLE 1 Moisture Pick-up Ex / Comp Particle size μ (g/kg) % Avoxrecovery 1 600-850 10 50 2 425-600 10 32 3 250-425 10 19 C1 600-850 10038 C2 425-600 100 16 C3 250-425 120 0

From the Table, it can be seen that by employing sodium percarbonatewhich intrinsically has a particle size of mean around 500 or higher incombination with a low moisture pick-up, it had a stability in thepresence of zeolite builder which was significantly and measurablyhigher than if only one of the two parameters had been selected alone.In particular, it will be observed that the stability of percarbonatehaving a very similar particle size range/distribution differedmarkedly, even though from the disclosure of EP451893 products of thesame particle size range (since neither had been coated to modifystability) would be expected to be likewise very similar; eg the productin Ex2 was twice as stable as the product in C2. The improvement in Avoxretention by employing percarbonate having low as compared with highmoisture pickup was consistently around 14 to 18% in the test. This canbe seen by comparing samples with the same fraction of particle sizes egEx2 with C2, and likewise, the improvement from selecting largerparticles is maintained in the range of 14 to 18% as can be seen bycomparing the results from within the respective Examples Ex1, Ex2 andEx3.

The results demonstrate clearly that the process of selecting sodiumpercarbonate based on the twin measurement of moisture pickup andparticle size represents a practical method of selecting sodiumpercarbonate that is intrinsically suitable for incorporation indetergent compositions, ie the selection of the materials in Examples 1and 2.

In a further set of tests, a sample of sodium percarbonate of the sametype as that employed before sieving in Examples 1 to 3 and having amoisture pick-up of 10 g/1000 g in the relevant test was contacted withfine particulate materials contemplated as coating agents. It was foundthat the effect of contacting with sodium carbonate, sodium sulphate andsodium silicate, even at 5% of that material did not increase therelevant stability determinant (moisture pickup) to more than about 15g/1000 g, but that the presence of 5% sodium chloride increased themoisture pick-up to over 100 g/1000 g confirming that preventing thepresence of an excess chloride content is highly important for retainingthe benefit of the inherent stability of the selected percarbonate ofthe invention in a subsequent coating operation.

In a further demonstration, the Avox stability was measured of samplesof sodium percarbonate in particulate mixture with a detergentcomposition containing a particulate zeolite A (Na salt) and a layeredsilicate (SKS-6) as builders, the test being conducted in wax laminatedboxes at 32° C. and 80% relative humidity. In trial 4, the sodiumpercarbonate had been produced by a method in essence like that whichproduced the products employed in Examples 1-3, ie an integralcrystalliser/classifier using sodium sulphate salting agent, but withthe operating conditions controlled to produce a product having a meanparticle size of about 750 μ and a moisture pick-up of <10 g/1000 g. Intest 5, a further sample of the sodium percarbonate used in test 4 wascoated with a 50/50 w/w mixture of sodium carbonate and sodium sulphateby damping the particulate percarbonate with a concentrated aqueoussolution of the coating agents in a laboratory scale agitated mixer atabout 25-30° C. to provide a total dry weight of 3% coating agents anddrying the damp percarbonate in a fluid bed drier.

In test C6 (comparative), the sodium percarbonate used was obtained bytaking a conventional “wet bed” product made using a chloride saltingout agent, (moisture pick-up of about 100 g/1000 g) and coating theparticulate material in the same way as in the product for test 5 with a50/50 w/w mixture of sodium carbonate and sodium sulphate (total 3% dryweight coating), the resultant material have a mean particle size ofabout 720 μ. The Avox recovered after 6 weeks storage for the testproducts was respectively

Test 4 43%

Test 5 65%

Test C6 32%

From the data above, it can be seen that in the presence of thezeolite/layered silicate, the uncoated percarbonate in test 4 was morestable by a significant amount than the coated product in test C6,confirming that by meeting a suitable combination of parameters inaccordance with the instant invention, a product of improved stabilitycan be obtained relative to percarbonate obtained conventionally, evenof similar particle size after coating. Secondly, it can be seen thatthe percarbonate in test 4 was a particularly suitable base for asubsequent coating, in that the coating also further enhanced thestability of the percarbonate. Even though the coating level was thesame in tests 5 and 6 the stability of the coated product meeting theparticle size and moisture pick-up criteria of the inventioncompositions was twice as good as that of the comparison coated product.

EXAMPLE 7 AND COMPARISON 8

In this Example, the tests for particle size and moisture pick-up wereconducted on two samples of sodium percarbonate which had been producedby reaction between a concentrated solution of hydrogen peroxide andsodium carbonate in bulk and precipitation therefrom in the presence ofa low concentration of diphosphonic acid stabiliser, and sodiumsilicate, polyacrylate and pyrophosphate crystal habit modifiers, but inthe absence of a salting out agent.

The moisture pick-up test was conducted in the same way as previouslydescribed herein and produced results of 14.1 and 10.7 g/kg in 24 hoursstorage, demonstrating that they are within the acceptable range ofbelow 30 g/kg. The particle size distribution was obtained by sievingthrough a nest of standard sieves, and this showed that the meanparticle size was respectively 723 and 747 μm, and that less than 7% ofthe particles were below 425 μm. This product passes the selectionprocess.

By comparison in C8, the same tests were conducted on a sample ofstandard commercially available sodium percarbonate obtained using aconventional salting out process. This comparison picked up 122 g/kgmoisture in 24 hours and had a mean particle size of 465 μm. This samplefails the selection process.

Further samples of the Example and comparison products were then mixedwith reference detergent A in the weight ratio of 15%:85%, and stored inpolyethylene-coated boxes in a constant temperature enclosure maintainedat 32C and 80% relative humidity. The active oxygen content of thecompositions was measured periodically by the standard titration methodand compared with the initial measurement to determine the proportion ofactive oxygen which had been retained.

Detergent A contained approximately 7.5% sodium linear alkyl benzenesulphonate, 25% zeolite A, 4% ethoxylated tallow alcohol, 3% soap, 5%SIK foam inhibitor, 9% sodium carbonate, 6% sodium sulphate, and anumber of detergent adjuncts including a proteyte enzyme, soilredeposition agent, optical brightener in minor amounts.

TABLE 2 Avox retained after 6 weeks Detergent A Example 7 66 Comparison8 18

From Table 2, it can be seen that sodium percarbonate selected inaccordance with the twin tests demonstrated significantly superiorstability.

Further testing on other zeolite-containing detergent compositionscontaining a bleach activator, tetraacetyl ethylenediamine (3%)confirmed that the sodium percarbonate selected in accordance with thetwin tests retained its avox longer than for sodium percarbonate whichdid not satisfy the twin tests.

EXAMPLE 9 AND COMPARISON 10

In this Example, a further sample of sodium percarbonate was tested thathad been produced by the same general method as for Example 7. In themoisture pick-up test, it picked up 7.6 g/leg in 24 hours. The particlesize was measured as for Example 7 and showed a mean particle size of716 μm, and 10% below 425 μm. Thus, this sample passed the twin tests.

Its stability in a detergent composition B was tested against a furthersample of the sodium percarbonate described in Comparison 8, in amixture of 20% sodium percarbonate to 80% base detergent, in the sameway as for Example 7.

The base detergent B contained approximately 8% linear alkyl benzenesulphonate, 3% ethoxylated tallow alcohol, 3% soap, 44% sodiumtripolyphosphate, 7% sodium silicate, 20% sodium sulphate, and soilantiredeposition agent and chelate in minor amounts.

TABLE 3 Avox retained after 6 weeks Detergent B Example 9 72 Comparison10 62

From Table 3, it can be seen that the benefit of selecting sodiumpercarbonate that intrinsically passes the twin tests is also apparentin compositions that are built with a phosphate builder, although thedifference is not as great as for zeolite-built compositions.

A further sample of the sodium percarbonate described in Example 9 wascoated with 3% by weight sodium carbonate/sodium sulphate (but 2:1weight ratio) in the manner described for Example 5. The avox stabilityresultant product was then tested in reference detergent A in the sameconditions as for Example 7. It was found that after 6 weeks storage,70% avox had been retained, indicating that the coating had furtherimproved the storage quality of core sodium percarbonate thatintrinsically passed the twin tests.

EXAMPLES 11 TO 13

In these Examples, washing compositions are obtained by dry blendingsodium percarbonate obtained by operation of a crystallisation processin which sodium percarbonate precipitated from a solution containinghydrogen peroxide and sodium carbonate in a mole ratio of 0.85:1 andinto which no additional salting out-agent was introduced, the producthaving the properties of 7 day aged heat emission (LKB) of <3 μW/g in 16hours, water pick-up (MPU) of 10 g/1000 g, mps (mean particle size) of770 μ (span 1.0) bulk density (BD) 920 g/1000 g into a pre-formedmixture of the remaining constituents. The constituents and theirrespective proportions are summarised in Table 4 below.

In Table 4, ABS indicates sodium alkyl benzene sulphonate, AEO alcoholethoxylate, other surfactant includes a soap , and/or a cationicsurfactant, the bleach activator is tetra acetyl ethylene diamine, orsodium nonanoyl or acetyl oxybenzenesulphonate and the detergentadjuvants include one or more polycarboxylate or polyphosphonatecomplexing builder, one or more cellulose derivatives, PVP and/or maleicanhydride copolymers acting as soil anti redeposition agents, anaminostilbene optical brightener, colorant and perfume and optionally anamylase, protease lipase esterase or cellulase enzyme.

TABLE 4 Example No 11 12 13 Amount % w/w anionic surfactant - ABS 9 15 7nonionic surfactant - AEO 4 3 3 other surfactant 9 3 Zeolite 4A 28 20 Natripolyphosphate 37 Na carbonate 10 14 Sodium Percarbonate 15 20 15Bleach Activator 3 Sodium Sulphate 6 18 17 Detergent adjuvants 9 3 8

Similar compositions are obtainable by varying the amounts ofconstituents listed above, within the ranges known within the detergentindustry to remain effective, and by replacing all or part of individualconstituents, such as by replacing all or a fraction of the ABS with analkyl sulphate, alcohol sulphate, sulphate glyceride or succinate orphosphate esters, and/or by replacing the AEO at least in part by anethoxylated alkyl phenol, a PEO/PPO copolymer or fatty acid/amidepolyols and/or by replacing zeolite 4A with SKS6, or MAP zeolites and/orpartly with sodium silicate, and/or by replacing at least partlytripolyphosphate with sodium tetraphosphate and/or by replacing thediluent sodium sulphate with sodium chloride.

The sodium percarbonate incorporated in the compositions of each ofExamples 11 to 13 respectively can be varied by employing the followingpercarbonate products (P1 and P2) which were obtained in a crystalliseroperated without salting out agent and which intrinsically meet theparameters of low heat emission, low moisture pick-up and acceptablemean particle size.

TABLE 5 Product Ref P1 P2 P3 MPU g/1000 g 14 1.5 9.4 LKB μW/g 1 2 2.3MPS μm. 680 650 950 span 1.0 not measured 0.9 BD g/1000 g 990 notmeasured 900 Avox % 14.7 14.9 15.0

Further examples of PCS (P4 to P7) which can be employed instead ofproducts P2 or P3 comprise products made in the same apparatus undervaried operating conditions, whilst still avoiding addition of a saltingout agent, and which the acceptable low MPU (<30 g/1000 g) and low 7 dayaged LKB of <3 μW/g in 16 hours and the other physical characteristicslisted below in

TABLE 6 Product Ref P4 P5 P6 P7 MPS μm. 680 770 840 700 span 1.1 1.2 1.01.2 BD g/1000 g 930 920 920 860 Avox % 15.0 14.8 15.0 14.4

The PCS can be further varied by employing such products which areintrinsically acceptable as the core for a coating, for example in anamount of from 2 to 5% w/w (particularly 3%) of sodiumsulphate/carbonate, sodium borate/silicate, or coating agents contactedin acid form such as a mixture of boric acid with neutral salts such assodium sulphate and/or chloride and optionally a carboxylic acid and/orhydroxycarboxylic acid capable of forming a complex with an oxy-boroncompound, or especially using mother liquor containing added sodiumsulphate to a mole ratio of Na₂CO₃:Na₂SO₄ of from 1:2 to 2:1.

The compositions will demonstrate varied rates of decomposition of thesodium percarbonate, but all will enjoy the benefit of employing thereadily bulk storable PCS and the stability offered by a large particlesize in comparison with the use of PCS that does not meet either or bothof the twin features of low heat emission and large particle size.

What is claimed is:
 1. Sodium percarbonate intrinsically having a meanparticle size of from 500 to 1200 microns and no more than 20% by weightof a particle size below 350 microns and a moisture pick-up whenmeasured in a test at 80% relative humidity and 32° C. after 24 hours ofnot greater than 30 g/1000 g sample.
 2. A sodium percarbonate accordingto claim 1 intrinsically having a mean particle size of from 500 to 850microns.
 3. A sodium percarbonate according to claim 1 intrinsicallyhaving a moisture pick-up of not more than 15 g/1000 g when measured insaid test.
 4. A sodium percarbonate according to claim 1 being coatedwith a layer of from 1 to 20% by weight of an inorganic and/or organiccoating.
 5. A sodium percarbonate according to claim 4 wherein thecoating layer comprises no more than 2.5% by weight chloride calculatedas NaCl based on the sodium percarbonate.
 6. A sodium percarbonateaccording to claim 1 obtained by crystallization from ahalide-restricted saturated aqueous solution.
 7. A sodium percarbonateaccording to claim 6 is obtained by crystallization from solution byaddition of a non-halide sodium salting agent.
 8. A sodium percarbonateaccording to claim 6 obtained by crystallization from solution in theabsence of a salting agent.
 9. A sodium percarbonate according to claim6 classified to remove undersize and oversize particles and retain aproduct having the particle size characteristics of claim
 1. 10. Asodium percarbonate according to claim 9 wherein the crystallization andclassification of the sodium percarbonate occur in a classifyingcrystallizer.
 11. A sodium percarbonate according to claim 1 having a 7day aged heat emission at 40° C. of below 3 μW/g in 16 hours.
 12. Asodium percarbonate according to claim 1 having an Avox of at least14.5%.
 13. A sodium percarbonate according to claim 1 having a bulkdensity of 800 to 1000 g/1000 cm³.
 14. A detergent compositioncomprising a builder and sodium percarbonate according to claim
 1. 15. Adetergent composition according to claim 14 comprising from 2 to 40% byweight sodium percarbonate.
 16. A detergent composition according toclaim 14 comprising from 5 to 60% builder.
 17. A detergent compositionaccording to claim 14 comprising at least one activator which reacts inaqueous solution with sodium percarbonate to generate a peroxyacid. 18.A detergent composition according to claim 14 wherein said buildercomprises a zeolite builder.
 19. A detergent composition according toclaim 14 containing a phosphate builder.
 20. A method of selectingsodium percarbonate for incorporation in a builder-containingcomposition comprising: 1) measuring particle size distribution of saidsodium percarbonate, determining its mean particle size and the weightfraction below 350 microns, and rejecting material having either a meanparticle size outside the range of from 500 to 1200 microns orcontaining more than 20% by weight of particles having a size below 350microns; and 2) measuring the extent to which moisture is picked up bythe material in a test conducted for 24 hours at 32° C. and 80% relativehumidity and rejecting material which picks up more than 30 g moistureper 1000 g material.